The rush to move asylum seekers from Christmas Island to Nauru and Manus Island may place lives at risk and has compromised the ethical and medical responsibilities of healthcare professionals, according to serious allegations in a letter documenting a first-hand account of the process.

The letter of concern, obtained exclusively by Guardian Australia, outlines how key medical tests were abandoned, first by Labor and then by the Coalition, to meet tighter and tighter deadlines to move asylum seekers offshore.

Tony Abbott first mentioned the 48-hour turnaround when the newly restored prime minister Kevin Rudd announced he would be processing all single males and sending them to Manus and Nauru within a fortnight.

“Will they be sent within 24 or 48 hours of arriving in this country?"

Labor declared that target impossible to meet, citing, among other things, health concerns. But when Scott Morrison became minister for immigration and border security two months later he mandated a 48-hour target turnaround for everyone.

“We're just not allowing people to settle in as the previous government did,” he said. “They won't be settling in Australia, they'll be going to Nauru or Manus Island and that's what they can expect.”

He said the only test would be whether the asylum seekers were “fit to fly”.

The letter of concern reveals that a number of key basic medical tests, designed to assess an asylum seeker’s appropriateness for being sent offshore, were abandoned in July. Asylum seekers no longer had their blood sugar levels tested nor their urine, resulting in scores of people who would normally be unsuitable for transfer slipping through the net, the letter documents.

After the election of the Coalition even more stress was placed on the medical screening process. Patients with blood disorders previously deemed to make them unsuitable for transfer were approved. All asylum seekers were liable to be moved offshore without their test results for diseases including Hepatitis B and HIV being returned.

“The brief and compromised health assessments have poor sensitivity for detecting significant medical problems,” the letter says. As a result transfers are occurring under time-intensive pressure with “so little information” that groups of individuals have been moved inappropriately, risking their own safety was well as broader public health.

The letter contains compelling case studies, including that of a boy with cerebral palsy who was sent to Nauru despite doctors placing him on the transfer list to receive specialist medical help on the Australian mainland.

The doctors have significant concerns that asylum seekers could be transferred offshore with tuberculosis.

The letter documents the case of a man declared as “fit for transfer” who was later diagnosed as having TB. Before that he spent more than a month in a Christmas Island detention centre. “Potentially the entire camp has been exposed,” the letter says.

Multiple requests for comment have been lodged with the minister. He is yet to respond.

Before July, the letter says, screening was “somewhat more acceptable as patients would undergo a period of surveillance within the detention centre in which abnormal results were followed up and any medical problems could be detected and/or further assessed by medical officers in clinics”.

The decision to transfer an asylum seeker offshore is now based on a stripped-down version of a health induction assessment. The HIA is the medical test asylum seekers undergo when they arrive. On some occasions – particularly when boats carrying a large number of people arrive – it can last less than five minutes, despite medical officers agreeing it must last a minimum of 20.

“Some doctors are required to perform up to 90 assessments in a single eight-hour shift (less than five minutes each),” the letter says. “Time pressures are compounded by the need for translators and for relevant data to be entered into the health information system.

“Time pressures and unsafe working hours can also impact on the quality and safety of assessments made by fatigued medical practitioners.”

After the HIA, a discharge health assessment is completed to allow for offshore transfer. These are completed by a reporting nurse with input from the medical director. But, according to the letter, “certifying medical clearance is not usually within the scope of practice for a registered nurse”.

It says neither the nurse nor medical director have seen the patient and are “basing the decision on a flawed and often incomplete HIA process with poor sensitivity in detecting medical problems”.

The letter says immunisations are rushed. This has resulted in “multiple vaccination errors, such as the administration of live vaccines to pregnant women and patients with inter-current illnesses. Furthermore, these patients are flown offshore to places of risk before these immunisations have had time to take effect.”

Guardian Australia has previously reported concerns from the Royal Australasian College of Physicians that inoculations would not have time to take effect as a result of rapid transfer. This was dismissed by Morrison, who has repeatedly said that doctors’ fears on the 48-hour turnaround were unfounded.

He added: “Inoculations, as I understand, it have always been done on Manus Island anyway.”

The letter of concern directly contests this point: “Immunisations are performed on Christmas Island prior to departure. Their hasty implementation resulted in administration of live vaccines to pregnant women.”

The letter also says blanket prescription of Malarone malaria pills occurs, “without the prescribing doctors ever seeing their patients”. The pills are prescribed after the HIA, which contains no questions about a patient’s sensitivity to the drug.

The letter raises significant concerns, which have been voiced by a number of agencies in the past, that medical facilities on PNG and Nauru are not equipped to deal with complex medical problems.

Guardian Australia has published a number of articles examining the serious concerns that medical experts have about the 48-hour turnaround time, but the evidence contained in the letter of concern is the most forensic portrayal of the severe risks involved in the process Morrison introduced.

The seven-page section detailing concerns about the 48-hour target ends by raising serious concerns that this “dramatic change in practice” represents a conflict of interest for the doctors’ employer, IHMS (International Health and Medical Services). It adds that the process also puts medical staff at “great medico-legal risk”.

“Management states that the Department of Immigration are accepting all responsibility,” it says. “However no third party has the power to absolve health practitioners of their duty of care to patients and we must adhere to AHPRAs [Australian Health Practitioner Regulation Agency] code of conduct.”

It recommends that the 48-hour target be abolished.

IHMS said it does not believe the 48-hour turnaround time puts the lives of asylum seekers at risk.

The private medical provider is examining the letter of concern. “IHMS values the contribution of all of our professional medical staff to ensure our care to people in detention remains of the highest standards,” it said.